FLORISSANT FLIES 

 More than a thousand different species of insects and plants have been found in the Florissant shales, many of 

 them, like the horseflies (Figs. 1 and 2 above) being very closely allied to living forms. The horses and other 

 animals which these insects must have persecuted were, however, very different from those of today, the mam- 

 malian groups having greatly changed since the Miocene while insects and plants have remained nearly the same. 

 Migrations that have taken place among the latter, make it possible to connect the presence or absence of certain 

 forms with changes of land and water. In the order numbered, the flies above are Tabanus parahippi, Tabanus 

 hipparionis, Psilocephala hypogxa, Lithocosmus coguillelti (a genus now extinct), and Chilosia miocenica 



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